feat(#95): implémenter la gestion Relais admin et le rattachement gestionnaire

Ajoute la section Paramètres territoriaux avec CRUD Relais, modale de saisie structurée, états visuels harmonisés, et rattachement d'un relais principal aux gestionnaires via l'API.

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/lib/services/relais_service.dart

@@ -0,0 +1,97 @@
+import 'dart:convert';
+
+import 'package:http/http.dart' as http;
+import 'package:p_tits_pas/models/relais_model.dart';
+import 'package:p_tits_pas/services/api/api_config.dart';
+import 'package:p_tits_pas/services/api/tokenService.dart';
+
+class RelaisService {
+  static Future<Map<String, String>> _headers() async {
+    final token = await TokenService.getToken();
+    return token != null
+        ? ApiConfig.authHeaders(token)
+        : Map<String, String>.from(ApiConfig.headers);
+  }
+
+  static String _extractError(String body, String fallback) {
+    try {
+      final decoded = jsonDecode(body);
+      if (decoded is Map<String, dynamic>) {
+        final message = decoded['message'];
+        if (message is String && message.trim().isNotEmpty) {
+          return message;
+        }
+      }
+    } catch (_) {}
+    return fallback;
+  }
+
+  static Future<List<RelaisModel>> getRelais() async {
+    final response = await http.get(
+      Uri.parse('${ApiConfig.baseUrl}${ApiConfig.relais}'),
+      headers: await _headers(),
+    );
+
+    if (response.statusCode != 200) {
+      throw Exception(
+        _extractError(response.body, 'Erreur chargement relais'),
+      );
+    }
+
+    final List<dynamic> data = jsonDecode(response.body);
+    return data
+        .whereType<Map<String, dynamic>>()
+        .map(RelaisModel.fromJson)
+        .toList();
+  }
+
+  static Future<RelaisModel> createRelais(Map<String, dynamic> payload) async {
+    final response = await http.post(
+      Uri.parse('${ApiConfig.baseUrl}${ApiConfig.relais}'),
+      headers: await _headers(),
+      body: jsonEncode(payload),
+    );
+
+    if (response.statusCode != 201 && response.statusCode != 200) {
+      throw Exception(
+        _extractError(response.body, 'Erreur création relais'),
+      );
+    }
+
+    return RelaisModel.fromJson(
+        jsonDecode(response.body) as Map<String, dynamic>);
+  }
+
+  static Future<RelaisModel> updateRelais(
+    String id,
+    Map<String, dynamic> payload,
+  ) async {
+    final response = await http.patch(
+      Uri.parse('${ApiConfig.baseUrl}${ApiConfig.relais}/$id'),
+      headers: await _headers(),
+      body: jsonEncode(payload),
+    );
+
+    if (response.statusCode != 200) {
+      throw Exception(
+        _extractError(response.body, 'Erreur mise à jour relais'),
+      );
+    }
+
+    return RelaisModel.fromJson(
+        jsonDecode(response.body) as Map<String, dynamic>);
+  }
+
+  static Future<void> deleteRelais(String id) async {
+    final response = await http.delete(
+      Uri.parse('${ApiConfig.baseUrl}${ApiConfig.relais}/$id'),
+      headers: await _headers(),
+    );
+
+    if (response.statusCode != 200 && response.statusCode != 204) {
+      throw Exception(
+        _extractError(response.body, 'Erreur suppression relais'),
+      );
+    }
+  }
+}